The present invention relates to a method and apparatus for edge finishing sheet materials. More particularly, the present invention relates to a method and apparatus for grinding and polishing the edges of sheet materials, such as glass sheets for use in flat panel displays which avoid damaging at least one surface of the sheet.
Processing of sheet of materials that require a high quality surface finish, for example, glass sheets for flat panel displays, typically involves cutting the sheet into a desired shape and then grinding and/or polishing the edges of the cut sheet to remove any sharp corners. The grinding and polishing step is usually carried out on apparatus known as a double edger or double edging machine. Such double edging machines are known and available from Bando Kiko Co., Ltd., Mitsubishi Heavy Industries, Fukuyama Co., and Glass Machinery Engineering.
During the grinding and polishing of the edges of the glass sheets on a double edging machine, the sheet is typically sandwiched between neoprene or rubber belts in contact with both surfaces of the sheet. The belts contacting both surfaces of the sheet cooperate to hold the sheet in place while the edges of the glass are ground or polished by an abrasive grinding wheel. The belts also transport the sheet through a feeding section of the machine, a grinding or polishing section of the machine, and an end section of the machine.
A typical belt arrangement for a double edging machine is shown in FIGS. 1 and 2. A glass sheet 10, is sandwiched between upper belts 12 and a lower belts 14. As shown in FIG. 2, there is usually a pair of upper belts and lower belts that cooperate to hold the sheet 10. The belts 12 and 14 are driven and supported by pulleys 16. In operation, the pulleys rotate in the directions shown in FIG. 1, causing the belts to transport the sheet in the direction shown.
The above described method of gripping and conveying a sheet of glass through a grinding/polishing machine has several disadvantages. Particles generated during edge finishing can contaminate and scratch the glass sheet. Particles and chips caught between the upper belt 12 and the glass sheet 10 can severely damage the surface of the glass. Sometimes the damage can be the cause of a break source in subsequent processing and result in poor process yields due to rejected product.
In view of the disadvantages mentioned above, it would be desirable to provide a method and apparatus for conveying and holding a sheet of material such as glass while the edges of the sheet are being finished without damaging the quality surface of the sheet. The method and apparatus should be capable of applying a force sufficient to prevent the sheet from moving away from the edge finishing device during the finishing process.
Accordingly, the present invention generally provides a method and apparatus for grinding or polishing the edges of a sheet of material, particularly glass sheets, comprising grinding or polishing at least one edge of the sheet using grinding or polishing device. The method and apparatus of this invention further includes supporting one surface of the sheet on a conveyor and holding the sheet on the conveyor by exerting a force on the sheet with a fluid pressure device. The fluid pressure device preferably creates a force sufficient to maintain the glass on a conveyor having an average coefficient of friction of 0.45 during grinding or polishing of the glass. In one embodiment the force to hold the glass is at least about 10 pounds, and preferably at least 20 pounds, which can be measured using a spring pullout gauge.
In one embodiment of this invention, the fluid pressure device for creating the holding force is maintained adjacent one major surface of the sheet. According to one aspect of the invention, the fluid pressure device creates a sub-atmospheric pressure, for example, a vacuum pressure. In another aspect, the device comprises a plurality of elements attached to the conveyor for creating the sub-atmospheric pressure.
In another aspect of the invention, the fluid pressure device which applies the holding force creates a positive pressure. According to one aspect of the invention, the positive fluid pressure device comprises a hydrostatic bearing. In another embodiment, the positive fluid pressure device comprises an aerostatic bearing positioned adjacent the side of the sheet opposite the conveyor.
Advantageously, the present invention provides a method and apparatus for holding a flat article, such as a sheet of glass, while the edges of the article are being finished, without marking or impairing the surface of the article. Additional features and advantages of the invention will be set forth in the description which follows. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
In the accompanying drawings, like reference characters denote similar elements throughout the several views. It is to be understood that various elements of the drawings are not intended to be drawn to scale, but instead are sometimes purposely distorted for the purposes of illustrating the invention.